Typically, high-energy ions generated in conventional etch processes that use plasma, such as reactive ion etching (RIE), are difficult to control within the plasma. Conventional RIE techniques are associated with several issues that hinder the overall performance in etching the substrate due to the lack of control of the high-energy ions. Conventional RIE techniques often have broad ion energy distribution (TED). A broad ion energy distribution decreases the precision required to adequately etch the substrate. Conventional RIE techniques also have charge-induced side effects such as charge damage to the substrate, and feature-shape loading effects such as micro loading. Micro loading results in an increase in etching rate due to a dense area of the substrate. The increased etching rate may result in non-uniform etching of the substrate.
It is becoming common wisdom to use conventional electron beam excited plasma to process substrates. Conventional electron beam excited plasma processes operate with direct current so that the electron beam density and energy are controlled independently by discharge current and accelerating voltage, respectively, due to the constant-voltage and constant-current characteristics. Therefore, the electron temperature and plasma density, as well as sheath potential, are easily controlled at the substrate as compared to other conventional plasma processes.
Conventional electron beam excited plasma processes implement a two chamber approach. An electron beam source chamber is used to generate the electron beam by exciting plasma within the electron beam source chamber. Hot filament discharge, hollow cathode discharge and inductively couple discharge (RF power) have been applied to the electron beam source chamber to excite plasma in the electron beam source chamber. The excited electrons in the electron beam source chamber travel through one or more differentially biased grids into the process chamber to generate plasma in the process chamber. A magnetic field is also applied to the process chamber to confine or enlarge the electron beam in the radial direction.
The electron beam excited plasma continues to process the substrate as long as the power supplied to the electron beam source chamber to excite the electrons is maintained. Thus, the power is continuously supplied to the electron beam source chamber during treatment of the substrate. The continuous supply of power to the electron beam source chamber has a significant impact on the power efficiency in treating the substrate. Therefore, an effective means to decrease the overall power used to maintain the strength of the electron beam while processing the substrate is needed.